1. Field of the Invention
The present invention relates to systems and methods for encoding and decoding data, and in particular to a system and method for generating and processing slice headers with high efficiency video coded data.
2. Description of the Related Art
There is rapid growth in the technologies associated with the generation, transmission, and reproduction of media programs. These technologies include coding schemes that permit digital versions of the media programs to be encoded to compress them to much smaller size and facilitate their transmission, storage, reception and playback. These technologies have application in personal video recorders (PVRs), video on demand (VOD), multiple channel media program offerings, interactivity, mobile telephony, and media program transmission.
Without compression, digital media programs are typically too large to transmit and/or store for a commercially acceptable cost. However, compression of such programs has made the transmission and storage of such digital media programs not only commercially feasible, but commonplace.
Initially, the transmission of media programs involved low to medium resolution images transmitted over high bandwidth transmission media such as cable television and satellite. However, such transmission has evolved to include lower bandwidth transmission media such as Internet transmission to fixed and mobile devices via computer networks, WiFi, Mobile TV and third and fourth generation (3G and 4G) networks. Further, such transmissions have also evolved to include high definition media programs such as high definition television (HDTV), which have significant transmission bandwidth and storage requirements.
The High Efficiency Video Coding (HEVC) coding standard (or H.265) is the most recent coding standard promulgated by the ISO/IEC MPEG standardization organizations. The coding standard preceding HEVC included the H.262/MPEG-2 and the subsequent H.264/MPEG-4 Advanced Video Coding (AVC) standard. H.264/MPEG-4 has substantially replaced H.262/MPEG-2 in many application including high definition (HD) television. HEVC supports resolutions higher than HD, even in stereo or multi-view embodiments, and is more suitable for mobile devices such as tablet personal computers. Further information regarding HEVC can be found in the publication “Overview of the High Efficiency Video Coding (HEVC) Standard, by Gary J. Sullivan, Jens-Rainer Ohm, Woo Jin Han and Thomas Wiegand, IEEE Transactions on Circuits and Systems for Video Technology, December 2012, which is hereby incorporated by reference herein.
As in other coding standards, the bit stream structure and syntax of HEVC compliant data are standardized, such that every decoder conforming to the standard will produce the same output when provided with the same input. Some of the features incorporated into the HEVC standard include the definition and processing of a slice, one or more of which may together comprise one of the pictures in a video sequence. A video sequence comprises a plurality of pictures, and each picture may comprise one or more slices. Slices include non-dependent slices and dependent slices. A non-dependent slice (hereinafter simply referred to as a slice) is a data structure that can be decoded independently from other slices of the same picture in terms of entropy encoding, signal prediction, and residual signal construction. This data structure permits resynchronization of events in case of data losses. A “dependent slice” is a structure that permits information about the slice (such as those related with tiles within the slice or wavefront entries) to be carried to the network layer, thus making that data available to a system to more quickly process fragmented slices. Dependent slices are mostly useful for low-delay encoding.
HEVC and legacy coding standards define a parameter set structure that offers improved flexibility for operation over a wide variety of applications and network environments, and improved robustness to data losses. Parameter sets contain information that can be shared for decoding of different portions of the encoded video. The parameter set structure provides a secure mechanism for conveying data that is essential to the decoding process. H.264 defined both sequence parameter sets (SPS) that describe parameters for decoding a sequence of pictures and a picture parameter set (PPS) that describes parameters for decoding a picture of the sequence of pictures. HEVC introduces a new parameter set, the video parameter set (VPS).
The encoding and decoding of slices is performed according to information included in a slice header. The slice header includes syntax and logic for reading flags and data that are used in decoding the slice.
Like its predecessors, HEVC supports both temporal and spatial encoding of picture slices. HEVC defines slices to include I-slices, which are spatially, but not temporally encoded with reference to another slice. I-slices are alternatively described as “intra” slice encoded. HEVC also defines slices to include P (predictive) slices, which are spatially encoded and temporally encoded with reference to another slice. P-slices are alternatively described as “inter” slice encoded. HEVC also describes slices to include bi-predictive (B)-slices. B-slices are spatially encoded and temporally encoded with reference to two or more other slices. Further, HEVC consolidates the notion of P and B slices into general B slices that can be used as reference slice.
Currently, the HEVC syntax includes provision for extensions to expand the capabilities or capacities of HEVC beyond the baseline. Such extensions include range extensions (RExt, scalability extensions (SHVC), and multi-view extensions (MV-HEVC). Extensions may be signaled in the VPS, SPS, PPS, or combination thereof.
High Efficiency Video Coding (HEVC) Range Extensions text specification: Draft 4,” published by the Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 13th Meeting: Incheon, KR, 18-26 Apr. 2013, by David Flynn et al, (hereby incorporated by reference herein) defines a PPS syntax that controlled the execution of multiple extension functions by use of extension function-unique flags uniquely associated with each extension function. However, such flags were not independently read. For example, a first flag signaling the execution of one extension function in the PPS syntax may be read within syntax that is only parsed and executed if another (second) flag for a previously executed extension function has a particular state or value (e.g. a flag may not read unless the previously read flag tests “true”). This is not problematic when the execution of an extension function is not desired unless the previous extension function syntax has been executed. But it is problematic in cases where it is desirable to control the parsing or execution of the extension functions independently. What is needed is an improved system and method for parsing syntax that permits the parsing of extension functions to be independently controlled. This disclosure describes such a system and method.